Universe. There are many competing theories about the ultimate fate of the universe. Physicists remain unsure about what, if anything, preceded the Big Bang. Many refuse to speculate, doubting that any information from any such prior state could ever be accessible. There are various multiverse hypotheses, in which some physicists have suggested that the Universe might be one among many or even an infinite number of universes that likewise exist.[11][12] Historical observation XDF size compared to the size of the Moon – several thousand galaxies, each consisting of billions of stars, are in this small view. XDF (2012) view – each light speck is a galaxy – some of these are as old as 13.2 billion years[13] – the visible Universe is estimated to contain 200 billion galaxies.
XDF image shows fully mature galaxies in the foreground plane – nearly mature galaxies from 5 to 9 billion years ago – protogalaxies, blazing with young stars, beyond 9 billion years. History Etymology, synonyms and definitions. Supernova. A supernova (abbreviated SN, plural SNe after "supernovae") is a stellar explosion that is more energetic than a nova. It is pronounced /ˌsuːpəˈnoʊvə/ with the plural supernovae /ˌsuːpəˈnoʊviː/ or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months.
During this interval a supernova can radiate as much energy as the Sun is expected to emit over its entire life span.[1] The explosion expels much or all of a star's material[2] at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave[3] into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. Nova means "new" in Latin, referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super-" distinguishes supernovae from ordinary novae which are far less luminous. Discovery[edit] Star. For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space.
Once the hydrogen in the core of a star is nearly exhausted, almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime and, for some stars, by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity (chemical composition), and many other properties of a star by observing its motion through space, luminosity, and spectrum respectively. The total mass of a star is the principal determinant of its evolution and eventual fate.
A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Solar System. Discovery and exploration Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica (1660) For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System. People believed Earth to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos,[11] Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system.[12] His 17th-century successors, Galileo Galilei, Johannes Kepler and Isaac Newton, developed an understanding of physics that led to the gradual acceptance of the idea that Earth moves around the Sun and that the planets are governed by the same physical laws that governed Earth.
Additionally, the invention of the telescope led to the discovery of further planets and moons. Planet. The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions. Although the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. By careful analysis of the observation data, Johannes Kepler found the planets' orbits were not circular but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology.
History Printed rendition of a geocentric cosmological model from Cosmographia, Antwerp, 1539 Babylon Greco-Roman astronomy India Medieval Muslim astronomy European Renaissance 19th century 20th century. Gravitational singularity. A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. These quantities are the scalar invariant curvatures of spacetime, which includes a measure of the density of matter. The two most important types of spacetime singularities are curvature singularities and conical singularities.[2] Singularities can also be divided according to whether they are covered by an event horizon or not (naked singularities).[3] According to general relativity, the initial state of the universe, at the beginning of the Big Bang, was a singularity.
Interpretation[edit] Many theories in physics have mathematical singularities of one kind or another. Equations for these physical theories predict that the ball of mass of some quantity becomes infinite or increases without limit. Types[edit] Curvature[edit] , which is diffeomorphism invariant, is infinite. Gravitational wave. In physics, gravitational waves are ripples in the curvature of spacetime that propagate as a wave, travelling outward from the source.
Predicted in 1916 by Albert Einstein to exist[1] on the basis of his theory of general relativity,[2] gravitational waves theoretically transport energy as gravitational radiation. Sources of detectable gravitational waves could possibly include binary star systems composed of white dwarfs, neutron stars, or black holes. The existence of gravitational waves is a possible consequence of the Lorentz invariance of general relativity since it brings the concept of a limiting speed of propagation of the physical interactions with it. Gravitational waves cannot exist in the Newtonian theory of gravitation, in which physical interactions propagate at infinite speed. Introduction[edit] In Einstein's theory of general relativity, gravity is treated as a phenomenon resulting from the curvature of spacetime. Linearly polarised gravitational wave . Plane.
And . Gravitation. Gravitation, or gravity, is a natural phenomenon by which all physical bodies attract each other. It is most commonly recognized and experienced as the agent that gives weight to physical objects, and causes physical objects to fall toward the ground when dropped from a height. During the grand unification epoch, gravity separated from the electronuclear force. Gravity is the weakest of the four fundamental forces, and appears to have unlimited range (unlike the strong or weak force). The gravitational force is approximately 10-38 times the strength of the strong force (i.e., gravity is 38 orders of magnitude weaker), 10-36 times the strength of the electromagnetic force, and 10-29 times the strength of the weak force.
As a consequence, gravity has a negligible influence on the behavior of sub-atomic particles, and plays no role in determining the internal properties of everyday matter. History of gravitational theory Scientific revolution Newton's theory of gravitation General relativity. Galaxy. Galaxies contain varying numbers of planets, star systems, star clusters and types of interstellar clouds.
In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Supermassive black holes reside at the center of most galaxies. They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy is known to harbor at least one such object.[5] Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology.
A common form is the elliptical galaxy,[6] which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms. Etymology[edit] The word galaxy derives from the Greek term for our own galaxy, galaxias (γαλαξίας, "milky one"), or kyklos ("circle") galaktikos ("milky")[11] for its appearance as a lighter colored band in the sky. "See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt. " Dark matter. Dark matter is invisible. Based on the effect of gravitational lensing, a ring of dark matter has been detected in this image of a galaxy cluster (CL0024+17) and has been represented in blue.[1] Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the universe.
The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe. Other than neutrinos, a form of hot dark matter, it has not been detected directly, making it one of the greatest mysteries in modern astrophysics. Astrophysicists hypothesized dark matter because of discrepancies between the mass of large astronomical objects determined from their gravitational effects and the mass calculated from the observable matter (stars, gas, and dust) that they can be seen to contain.
Overview[edit] Baryonic and nonbaryonic dark matter[edit] Observational evidence[edit] Dark energy. Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. Dark energy has been used as a crucial ingredient in a recent attempt to formulate a cyclic model for the universe.[8] Nature of dark energy[edit] Many things about the nature of dark energy remain matters of speculation. The evidence for dark energy is indirect but comes from three independent sources: Distance measurements and their relation to redshift, which suggest the universe has expanded more in the last half of its life.[9]The theoretical need for a type of additional energy that is not matter or dark matter to form our observationally flat universe (absence of any detectable global curvature).It can be inferred from measures of large scale wave-patterns of mass density in the universe.
Effect of dark energy: a small constant negative pressure of vacuum[edit] . Cosmos. Cosmos is the Universe regarded as an ordered system.[1] The philosopher Pythagoras is regarded as the first person to apply the term cosmos (Greek κόσμος) to the order of the Universe.[2] Cosmology[edit] Cosmology is the study of the cosmos in several of the above meanings, depending on context. All cosmologies have in common an attempt to understand the implicit order within the whole of being. In this way, most religions and philosophical systems have a cosmology.
In physical cosmology, the term cosmos is often used in a technical way, referring to a particular spacetime continuum within the (postulated) multiverse. Theology[edit] In theology, the term can be used to denote the created Universe, not including the creator. See also[edit] References[edit] External links[edit] Cosmic string. Cosmic strings are hypothetical 1-dimensional (spatially) topological defects which may have formed during a symmetry breaking phase transition in the early universe when the topology of the vacuum manifold associated to this symmetry breaking was not simply connected. It is expected that at least one string per Hubble volume is formed. Their existence was first contemplated by the theoretical physicist Tom Kibble in the 1970s. The formation of cosmic strings is somewhat analogous to the imperfections that form between crystal grains in solidifying liquids, or the cracks that form when water freezes into ice. The phase transitions leading to the production of cosmic strings are likely to have occurred during the earliest moments of the universe's evolution, just after cosmological inflation, and are a fairly generic prediction in both Quantum field theory and String theory models of the Early universe.
Theories containing cosmic strings[edit] Dimensions[edit] Gravitation[edit] Cosmic microwave background radiation. Temperature of the cosmic background radiation spectrum as determined with the COBE satellite: uncorrected (top), corrected for the dipole term due to our peculiar velocity (middle), and corrected for contributions from the dipole term and from our galaxy (bottom). The Sunyaev–Zel'dovich effect shows the phenomena of radiant cosmic background radiation interacting with "electron" clouds distorting the spectrum of the radiation. There is also background radiation in the infrared, x-rays, etc., with different causes, and they can sometimes be resolved into an individual source. See cosmic infrared background and X-ray background.
See also cosmic neutrino background and extragalactic background light. History of significant events[edit] 1896: Charles Édouard Guillaume estimates the "radiation of the stars" to be 5.6 K. 1926: Sir Arthur Eddington estimates the non-thermal radiation of starlight in the galaxy has an effective temperature of 3.2 K. [1] See also[edit] References[edit] Black hole. A black hole is defined as a region of spacetime from which gravity prevents anything, including light, from escaping.[1] The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole.[2] Around a black hole, there is a mathematically defined surface called an event horizon that marks the point of no return.
The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics.[3][4] Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater. Objects whose gravity fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. History General relativity.